Sources and scales of extreme ionospheric space weather in the European mid-latitudes

Abstract

Large magnetic storms in near geospace can trigger unusual ionospheric density variability over mid-latitude regions. It is important to know the generation mechanism and scales of such disturbances in order to understand and assess their potential impact on radio propagation. We study such extreme ionospheric space weather situations in two categories: 1) propagation phenomena, known as Large-Scale Traveling Ionospheric Disturbances (LSTID) whose energy sources is injected in high latitude regions, and 2) direct effects related to localized particle precipitation and imposed electric fields. The LSTIDs observed in 2023 showed density variations of 0.5-1TEC propagating from the polar latitude down to southern Europe, which was followed by a 50% decrease in density over a large area compared to the previous days. During the 2015 storm, local increases of several TECU with a horizontal extent of several tens of kilometers were observed in northern Germany, which are thought to be related to the extended auroral zone. We discuss possible energy sources for such extreme ionospheric density fluctuations